Accelerated Changes in Activities of Cell Wall Degrading Enzymes in Abscission Zones of Mulberry Leaves with 2-Chloroethylphosphonic Acid

Abstract

The effect of 2-chloroethylphosphonic acid (ethephon) on cell wall degrading enzymes in the abscission zones of mulberry leaves was investigated, and the activities of these enzymes in the petiole were determined. The activity of cellulase in the section proximal to the abscission zone was the highest among the three parts examined and lowest in the petiole. Enzyme activities in the abscission zones increased remarkably in late fall. On the other hand, endo-polygalacturonase decreased slightly. The activities of hemicellulase and pectinesterase rose slightly in fall. The activity of cellulase was abundant in the abscission zone of the lower leaves, while exo-poligalacturonase activity was higher in the upper leaves. The abscission of mulberry leaves was accelerated by ethephon treatment, and the activity of cellulase in the abscission zone increased markedly. By polyacrylamide gel electrophoresis, two kinds of isoenzymes were found. The enzyme band with Rm 0.16 increased slightly earlier than the other band. The activity of exo-polygalacturonase and hemicellulase increased by ethephon treatment. Endo-polygalacturonase and pectinesterase showed a slight decrease after ethephon treatment and did not correlate with abscission. The results obtained show that increases in cellulase, exo-polygalacturonase and hemicellulase are associated with natural abscission, and they chemically accelerate abscission of the mulberry leaf.